1. Field of the Invention
The present invention relates to a power converter, and more specifically relates to a control circuit of switching power converters.
2. Description of Related Art
Various power converters have been widely used to provide regulated voltage and current For the sake of safety reasons, an off-line power converter uses a transformer to isolate its primary side and secondary side. Because the reflected voltage of the transformer can be used for regulations, the controller of the power converter normally includes a voltage-detection terminal coupled to the transformer to detect the reflected voltage of the transformer. hi recent development, many control schemes have been disclosed, such as “Primary-side controlled feedback power converter” by Yang, et al, U.S. Pat. No. 6,853,563; “Close-loop PWM controller for primary-side controlled power converters” by Yang, et al, U.S. Pat. No. 7,016,204; in which the voltage-detection terminal is operated as a feedback input terminal. The object of the present invention is to provide a detection circuit using the voltage-detection terminal to sense the input voltage of transformer. Therefore, no further feedback input terminal is needed.